Optical economizer



May 13, 1941. A. J. HOLMAN OPTICAL :cououuaa Filed Aug. 3, 1938 2 Shun-Shut -1 u u a a a n E u a a a a My 13, 1941. A. J. HOLMAN OPTICAL ECONOIIZER FilOd Aug. 3. 1938 2 Sheets-Sheet 2 Patented May 13, 1941 UNITED STATES PATENT OFFICE 7 omcar. noonomzm Arthur-J. nd anastoramm. J.

' Application Aug-t a, loss, Serial No. 222,791

17 Claims.

My invention relates to apparatus for projecting on a screen a composite action image comprising, atany instant, images of several regulation fllm frames, the individual frame images dissolving in and dissolving out of the composite action image without "will! the luminosity of the composite image.- Such composite action image can be created by a projector of the optical rectifying type capable of projecting simultaneously and without flicker well-defined undistorted images of several iilm frames, when such projector is used in combination with my present optical economizer. The function of the" economizer is to register on the screen the multiple frame images emanating from the projector, which is preferably of the type described in Letters Patent of The United States No. 1,957,457 dated May 8, 1934. The present invention is principally an improved optical economizer and differs in several important respects from my former device disclosed in Letters Patent of Th United States No. 1,989,994 dated January 29, 1935. Another item in this invention is an improvement in the projector aperture unit which eliminates certain defects formerly present in the composite action image when projecting in additive three color.

It has been the special object of my invention to so construct and so position the elements of my improved optical economizer that the image distortion caused by my former design may be completely neutralized. It has also been my object to determine and deflne the position wherein the device should be placed to provide that sharpness of image cut-oi! so essential to prevention of flicker in the composite action image, particularly along the upper and lower margins of the screen. Further objects have been. to determine and use the smallest mirrors consistent with the requirements, also to eliminate certain undesirable multiple image efl'ects caused by the use in my former device of improper mirrors, also. to eliminate flicker when projecting the composite action image in additive three color. Other improvements over my former device will become apparent from the disclosures hereinafter set forth.

My invention may be best understood by reference tothe accompanying drawings in which- Fig. 1 is a diagram illustrating passage toward the screen of multiple image rays emanating from the projector.

Fig. 2.is a diagram illustrating passage of multiple image rays to the screen with my former optical economizer.

Fig. 8 is a diagram illustrating passage of multiple image rays to the screen with my present device wherein the pairs of mirrors are arranged in V-formation above and below the optical axis.

Fig. 4 shows the arrangement of fllm frames (pictures) and frame lines on a standard 35 mm. release print.

Fig. 5 illustrates a graphic method for determining proper angle for mirrors nearest the projector, also minimum length of these mirrors.

Fig. 6 is a diagram showing relation between objective opening, economizer position and frame line height.

Fig. 7 shows an aperture unit and optical rectifying system, and illustrates the position of fllm frames over the aperture when a rectifying lens element is centered on the optical axis.

Referring now more specifically to the drawings in which like letters and numerals indicate like parts, 0 represents the nodal point or equivalent center of the objective system (Fig. l), O is a second point on the optical axis and the lines 0a and 0a represent, diagrammatically only, the boundary lines of the ray bundles comprising the central frame imag projected to the screen 8 without deviation by the economizer mirrors. The lines Ob and Ob likewise bound the ray blmdles which would arrive above the screen S, and the lines 00 and 0c bound the ray bundles which would arrive below screen 8, were each of these groups of ray bundles not redirected by the economizer mirrors to the screen S. The boundary lines 0a, Ob, 0c etc. do actually bound the various ray bundles comprising the separate frame images at and in the vicinity of the screen S, but at all other positions the ray bundles pass beyond their respective diagrammatic boundaries because the projector objective has a clear opening of considerable diameter whereas diagrams are drawn as if all rays transmitted by the objective were passed through a pin hole located at the nodal point 0. The spaces Us and a'c represent the height at screen 8 of the image of the fllm frame lines.

Fig. 2 shows the eflect on ray boundaries bOb', 00a and cOc' (Fig. 1) of inserting between nodal point 0 and screen S my former economizer wherein mirrors A are arranged to intercept ray bundles comprising the upper and lower frame images and to deflect them away from the optical axis 0-0, and mirrors B are arranged to intercept these ray bundles a second time and to redirect them to screen S, at which plane a, b, and c coincide, also a, b and c coincide. In my Letters Patent for an optical economlzer I pointed out that the opening between the centrally disposed mirrors A must be large with respect to the diameter of the objective lens and, furthermore, that the economizer must be placed several feet forward of the objective lens. It will be observed that the mirrors B are positioned considerably farther from the optical axis than the mirrors A; in fact mirrors B are located some distance outside the angle included within the broken lines b and c'O. Therefore, from the position of mirrors B the aspect of screen S is quite different from its aspect along the normal (optical axis) OO', more especially because the mirrors A and B are necessarily several feet from the nodal point 0.

In my improved optical economizer the mirrors C (Fig. 3) are positioned to intercept the ray bundles comprising the upper and lower frame images and to deflect them toward the optical axis. Each of the mirrors D, coacting with a corresponding mirror C, is positioned across the optical axis from its coacting mirror C so as to intercept all ray bundles reflected by mirror C and to redirect them to the screen S. It is to be noted that the edge of each mirror C nearest to the optical axis 0-0 is the edge farthest from objective nodal point 0, also that the edge of each mirror D nearest to the the optical axis is spaced therefrom the same amount as the nearest edge of each mirror C, hence the aspect of screen S from mirrors D is very nearly the same as the aspect of the screen along the optical axis OO. This is the result of arranging mirror C and D in V formation.

The position of the economizerwith respect to the projector in my present apparatus, is determined partly by the dimensions of the film pictures and film frame line height. In Fig. 4, t represents the height of a film picture and 1- represents the height of a frame line. The point d along the projected beam 00 (Fig. at which the forward edge of lower mirror C is to be located is determined as follows: It has been pointed out hereinbefore that the intercept ac of angle a'Oc (Fig. 1) at the screen S represents the height of the frame line image at the screen. For any distance 0d (Fig. 5) from nodal point 0, the intercept de of angle a'Oc in the plane at right angles to optical axis O-O' represents, diagrammatically, the height of the frame line ray bundle at position d. The distance de divided by the height 1 (Fig. 4) of the frame line on the film gives the magnification ratio from the film to the most constricted portion (throat) of the economizer. For reasons hereinafter fully disclosed I prefer to locate my economizer at such position along the projected beam that intercept de is equal to 71/2 where h is the height of the clear opening in the objective. The magnification ratio, film to most constricted portion or throat of economizer is, therefore, 71/27". The throat of economizer subtends at O the angle bOc which includes the central frame image and two frame line images. In order words, the economizer throat passes ray bundles corresponding in height to film dimension t+2r (Fig. 4). The actual dimension of the economizer throat is, therefore (t+2r), multiplied by the magnification ratio h/2r, or

The distance from the nodal point 0 to the throat of thei coiiomizer, measured along the optical axis OO', is equal to the distance from the film to the nodal point 0 multiplied by the magnification ratio h/2r. For ordinary projection distances the spacing from film to nodal point 0 is slightly more than the equivalent focal length of the objective, hence the economizer throat is spaced from the nodal point 0 slightly more than the equivalent focal length of the objective multiplied by h/2r. In newly processed standard release prints on mm. film t is .60 and r is .15" (very nearly), and if height h of the clear opening in the objective is 2.4", the height of the opening through the economizer throat is then or 7.2". If the equivalent focal length of the objective is 5", the economizer throat is spaced from the nodal point approximately or To state the rule then: The economizer is placed at such position that its most constricted portion (throat) will just pass the projected beam bOc (central frame plus two frame lines) the minimum spacing between the mirrors C (Fig. 3), also between mirrors D, is

and the economizer is spaced from nodal point 0, h/2r multiplied by the distance from film to nodal point 0.

The angular position of mirror C (Fig. 5) is determined graphically in the following manner. Just as the forward edge of lower mirror C is located at point d on line 00 so also is the forward edge of upper mirror C located at the corresponding point I on line 01). The lower mirror C must intercept all rays within the angle 00c, moreover the extreme lower ray 00' when intercepted at g by mirror C must be reflected through the opening fd in order to reach upper mirror D the rear edge of which parallels the forward edge of upper mirror C and is spaced therefrom only enough to allow clearance for angular adjustment of the mirrors. From Fig. 5 it is obvious that mirror C will have the shortest length dg when beam 00 is reflected at g and becomes beam of. The problem is then, to determine point 9 at which beam 00' when reflected by mirror C becomes beam of, and the solution is as follows. Using point d as center and distance (if as radius strike the arc flcl intersecting line 00 at Z; bisect the angle fdl with line km passing through d and interesecting line 00 at g. The law of reflection states that the angle of incidence Ogm is equal to the angle of reflection fgd. Obviously angle Ogm equals angle dgl. By construction, angle dgl equals angle fgd, therefore Ogm equals angle font and the mirror C is the shortest mirror which will intercept all of the beam 000 and direct all the intercepted beam through the opening Id. Upper mirror C is, of course, set in a symmetrical position with respect to lower mirror C above the optical axis OO'.

Lower mirrors C and D are preferably hinge mounted in V-formatlon on the axis d, likewise upper mirrors C and D are hinge mounted on axis ,f. Upper mirror D is positioned at such angle with respect to the optical axis OO as to reflect beam of (Fig. 5) to the bottom edge of the screen, point a (Fig. 3). Mirrors C and D must,

of course, be wide enough to intercept and deflect the full width. at the mirrors. of the projected beam. and, since mirror D is farther from the projector than mirror C, mirror I) must be somewhat-wider. The length of the mirrors is a function of the focal length of the objective; the horter the focal length the shorter the mirrors, but'mirrors will not vary greatly in length over focal lengths fmmd generally in the objective focal length is mirror C will be approximately long (length M Fig. ii) and mirror D will need to be about long.

The mirrors are made preferably of heavy plate glass -reground and highly polished on one side to a good optical flat and aluminired or otherwise made highly reflective on this surface. To avoid ghost images which would mar the composite action image, it is essential that first surface mirrors beused. Mirrors C and D must be so mounted "and supported as to avoid strains that would warp the optical flat reflecting surfaces. Mirrors C and D are preferably beveled where their edges are adjacent (axes d and I Fig. 5) to the clearance required for angular adjustment.

: It has been stated hereinbefore that the economiser is located at such position along the prolected beam that the intercept the heisht of the or half the height of the clear jective. In Fig. 6, n is a point of! the optical axis 0-0 such that n0 equals half the height h of the clear opening through the objective. Line Oeo' represents a ray passin through nodal point 0 to the extreme lower edge of the screen. a of the screen this is possible only if edge mirrors lies below line no. If p is the projection distanceand q is the econcmiser distance. both measured from nodal point 0. we have then in triangle Qa'n 7-1 But for ordinary theatre conditions q is quite small with respect to p, hence we have for all practical purposes. 40 equal to n0, which is the condition for prevention of flicker in the composite action image at the upper and lower margins conjunction withthe eoniln scribedinutters before referred to,theoosapolite satisfactoryand ubstanthlly blackandwhiteor nibtractiveeolormnch as'rschnieoloaarebeing'eshihitedalsoworkswellfortwocolor ing alternate frames dyed with colors. However. when I n wanwheel elements 4 is shown centered on the optical axis O'-O. The lines convers nfl m 9 bottom of the aperture 2 toward lens wheel component 4 and then divergl i th ug m component I, represent the envelop 0! we projected throu h pe 3 by the condenser system, which is preferably of the typ in Letters Patent of the United States No. 2,150,165 issued March 14, 1939. The film overlying the aperture is represented at t and a fllmframetisoenteredontheopfiealaxls- Film frameel and!arealsofullytxl l aperturebutframess and. i0 arepartlyecllp by the aperture unit. The black areas Ii representframeiinesseparatingthefllmpictureareas. Toavoidfiicheroverallareasinthe mpoalte actionimage,1have found aperturefnnistbe of suehhsightthat incoming frame It, advancing over part of frame 1 becomes eclipsed by the lower edge of aperture frame I. Thisconditioncannotobtainwithanapertm'e wbichisiessinheightthanfourfllmpioture area-splusthreeframeiines. Withanaperture threeframesinheightthereisacyclicparflal eclipsing of incoming and outgoing frames and. of course. the econonrizer cannot possibly deliver to the screenthecolor oomponentsessentialto the composite action image when these components are not supplied by the prolector.

The advantages of my present optical economisarareapparentfromanexaminationofllgs. 2and3. MirrorsAinmyformerdevicedefleet the upper and lower frame image rays am from. the optical axis whereas mirrors 0 deflect these rays toward and across the optical axis. The mirrors 3 which are necessarily quite some distance from the optical axis, produce at the screen considerable keystone effect in the images which they direct to the screen. This keystenlng of images is opposite in direction for upper and lower frame images and causes a lack of regimtion in the composite image which grows worse toward the corners of the screen. Another defeet causedbythiskeystnninglsanoutoffoeus condition in the deflected images toward the upper and the lower margins of the screen. This is due to the diflerence in projection distance, via mirrors B, to the top and to the bottom of the screen. By arranging mirrors C and D in V- formation at substantially equal distances from the optical axis, the keystonlng effect is greatly reduced. Moreover, by deflecting the upper and the lower frame images across the optical axis the keystoning effect of mirrors 0 is almost neutralized by mirrors D, hence registration in the composite action image is excellent even to the corners of the screen. The angular projec tion from mirrors D is only slightly different from the axial projection of the central frame image. hence the out of focus effect toward the top and bottom of the screen is not apparent. The present optical economizer combined with my single lens wheel projector having an aperture four frames in height, can create a highly satisfactory composite action image in natural color using a three color additive print whereon the filters are stained over the picture areas.

Having thus fully described my invention, what I claim is- I. An optical economizer of the character specifled comprising two pairs of mirrors, the first pair being positioned symmetrically adlacent the optical axis and adapted and arran ed to deflect the upper and lower frame images in such aperture I before any manner that they will cross from a position above to a position below said optical axis or vice versa, the second pair of mirrors also being placed symmetrically adjacent the optical axis, edge to edge with said first pair of mirrors and at such angle thereto as to cause said upper and lower frame images to register on the screen.

2. An optical economizer of the character specified comprising two pairs of mirrors arranged symmetrically in v-formation, one pair above and one pair below the optical axis, the V-edges being opposite and equally spaced from said optical axis, the angle between the mirrors nearest the projector being such as to cause the upper and lower image ray bundles to pass between said pairs of mirrors arranged in V-formation, and the angle between the mirrors farthest from the projector being such as to cause the upper and lower images to register on the screen with the central image.

3. An optical enonomizer of the character specified comprising two pairs of mirrors positioned symmetrically above and below the optical axis and adapted and arranged to constrict the multiple image ray bundles to the central passage through said economizer, said central passage being of such height as to pass the central ray bundle comprising the central frame image plus a frame line above and a frame line below said central frame image. a

4. An optical economizer of the character specified comprising two pairs of mirrors arranged symmetrically in V-formation, one pair above and one pair below the optical axis, the most constricted passage between said pairs of mirrors being equal in height to a film picture and two frame lines multiplied by the magnification ratio from film frame to economizer, said most constricted passage being spaced from the objective nodal point by an amount equal to the distance from nodal point to film multiplied by said magnification ratio.

5. An optical economizer of the character specified comprising two pairs of mirrors arranged symmetrically in V-formation, one pair above and one pair below the optical axis, the most constricted passage between said pairs of mirrors subtending an angle at the objective nodal point including ray bundles comprising the central frame image plus two frame lines, said most constricted passage being spaced from said nodal point by an amount equal to the distance between film and objective nodal point multiplied by one half the height of the clear opening through the objective and divided by the height of a film frame line.

6. An optical economizer of the character specified comprising two pairs of mirrors arranged symmetrically in V-formation, one pair above and one pair below the optical axis, the most constricted passage between said pairs of mirrors having a height equal to the height of a film picture and two frame lines multiplied by one half the height of the clear opening through the objective and divided by the height of a film frame line, said most constricted passage being spaced from the objective nodal point by an amount equal to the distance between film and nodal point multiplied by one half the height of the clear opening through the objective and divided by the height of a film frame line.

7. An op ical economizer of the character spccified comprising two pairs of mirrors arranged symmetrically in V-formation, one pair above and one pair below the optical axis, the mirrors nearest the projector being positioned at such angle to said optical axis as to cause the extreme tral frame image.

8. An optical economizer of the character specified comprising two pairs of mirrors positioned symmetrically in V-formation, one pair above one pair below the optical axis, the mirrors nearest the projector being adapted and arranged to intercept the upper and lower frame image rays, the angle and spacing between these mirrors being such as to cause the reflected ray bundles from each mirror to just fill the most constricted passage between said mirrors, and the central frame image.

9. An optical economizer of the character specifled comprising two pairs of first surface mircross from a position above to a position below said optical axis or vice versa, and to register on the screen with the central frame image projected through said economizer without reflec- 10. An optical economizer of the character specified comprising two 12. combination, a projector of the optical rectifying, type having an aperture four frames in strip of the three color additive type having filters stained in the film frames and of saturated primary colors.

13. In combination, a projector of the optical ectifying type having an aperture four frames film strip of the three color additive stained in the film frames in height, a type having filters pair being positioned one above and one below and moving continuously over said aperture, and an optical economizer of the character specified comprising two pairs of first surface mirrors arranged symmetrically about the optical axis in V-formation forward of the objective nodal point, said mirrors being proportioned and positioned to intercept all upper and lower frame image ray bundles, to reflect them through the opening between the mirrors traversed by the central frame image and to register said upper and lower frame images on the screen with said central frame image, thereby recreating continuously on the screen an image possessing the composite color values recorded on the film.

14. An optical economizer positioned forward of the objective nodal point and arranged to register multiple frame images on a screen in the manner spe ified, said optical economizer comprising two pairs of mirrors positioned symmetrically about the optical axis and arranged to neutralize the keystone eifect in the reflected images by causing all ray bundles deviated by said mirrors to cross from positions above to positions below said optical axis, or vice versa.

15. An optical economizer positioned forward of the objective nodal point and arranged to register multiple frame images on a screen in the manner specified, said optical economizer comprising two pairs of mirrors, the mirrors of a coacting the optical axis to neutralize the keystone effect in the reflected images by causing all deviated ray bundles to cross from positions above to positions below said optical axis, or vice versa.

16. An optical economizer positioned forward of the objective nodal point and arranged to register multiple frame images on a screen in the manner specified, said optical economizer comprising two pairs of mirrors arranged symmetrically in V-formation, one pair above and one pair below the optical axis, said pairs of mirrors being spaced from each other and from the objective nodal point in a manner whereby mirrors of the smallest dimensions may be used without causing any luminous area of the objective to be eclipsed by the economizer over any area of the screen.

17. An optical economizer positioned forward of the objective nodal point and arranged to register multiple frame images on a screen in the manner specified, said optical economizer comprising two pairs of mirrors positioned adjacent the optical axis and arranged to minimize the difference in projection distance via said mirrors from nodal point 0 to the top and to the bottom of the screen by directing the central rays of each film frame toward the optical axis whenever said rays are reflected.

ARTHUR J. HOLMAN. 

